Mutagenesis and analysis of genetic mutations in the GC-rich KISS1 receptor sequence identified in humans with reproductive disorders

The kisspeptin receptor (KISS1R) is a G protein-coupled receptor recognized as the trigger of puberty and a regulator of reproductive competence in adulthood (1,2,3). Inactivating mutations in KISS1R identified in patients have been associated with iodiopathic hypogonadotropic hypogonadism (IHH) (1,2) and precocious puberty (4). Functional studies of these mutants are crucial for our understanding of the mechanisms underlying the regulation of reproduction by this receptor as well as those shaping the disease outcomes, which result from abnormal KISS1R signaling and function. However, the highly GC-rich sequence of the KISS1R gene makes it rather difficult to introduce mutations or amplify the gene encoding this receptor by PCR. Here we describe a method to introduce mutations of interest into this highly GC-rich sequence that has been used successfully to generate over a dozen KISS1R mutants in our laboratory. We have optimized the PCR conditions to facilitate the amplification of a range of KISS1R mutants that include substitutions, deletions or insertions in the KISS1R sequence. The addition of a PCR enhancer solution, as well as of a small percentage of DMSO were especially helpful to improve amplification. This optimized procedure may be useful for other GC-rich templates as well. The expression vector encoding the KISS1R is been used to characterize signaling and function of this receptor in order to understand how mutations may change KISS1R function and lead to the associated reproductive phenotypes. Accordingly, potential applications of KISS1R mutants generated by site-directed mutagenesis can be illustrated by many studies (1,4,5,6,7,8). As an example, the gain-of-function mutation in the KISS1R (Arg386Pro), which is associated with precocious puberty, has been shown to prolong responsiveness of the receptor to ligand stimulation (4) as well as to alter the rate of degradation of KISS1R (9). Interestingly, our studies indicate that KISS1R is degraded by the proteasome, as opposed to the classic lysosomal degradation described for most G protein-coupled receptors (9). In the example presented here, degradation of the KISS1R is investigated in Human Embryonic Kidney Cells (HEK-293) transiently expressing Myc-tagged KISS1R (MycKISS1R) and treated with proteasome or lysosome inhibitors. Cell lysates are immunoprecipitated using an agarose-conjugated anti-myc antibody followed by western blot analysis. Detection and quantification of MycKISS1R on blots is performed using the LI-COR Odyssey Infrared System. This approach may be useful in the study of the degradation of other proteins of interest as well.